Damage induced by 90 MeV silicon ions in crystalline silicon

Abstract

Samples of n-type crystalline silicon were exposed to different fluences, ranging from 1.25 to 5×1014 ions/cm2, of 90 MeV silicon ions. The induced disorder in the surface region was studied by grazing-angle x-ray-diffraction and optical reflection spectroscopy, and that in the bulk was studied by measuring the lifetime of the excess minority carriers generated by a 1 MeV pulsed electron beam. Both in the surface region, as well as in the bulk, the degree of induced lattice defects was found to increase with an increase in the ion fluence. The value of the damage coefficient, estimated from the lifetime of the minority carriers, gradually increased from 1.2×10−10 to 8.9×10−10 cm2 s−1 over the range of ion fluences. These results indicate that 90 MeV silicon ions create an appreciable number of defects in crystalline silicon, the concentration of which increases from the surface to their projected range of ∼31 μm, and at higher fluences secondary defects are also produced in the bulk. Even at the highest fluence used the energy deposited through electronic loss had no observable effect on annealing the induced defects.